Introduction

The Sahel is one of the most investigated areas in Africa because of its highly complex and sensitive human and environmental dynamics. The Sahel is a transition zone between the pure desert of Sahara and the woody savanna of the Sudanean zone further south. It is a very fragile ecosystem where the signals of climate change and climate variability have been most apparent, with unprecedented climate variability over the last four decades (Hiernaux et al., 2009; Kaptué, Prihodko, & Hanan, 2015). The Sahel has gone through major drought sequences since 1970s, and deficient rainfall has been flagged as a Sahel crisis (Mortimore & Adams, 2001). Over 5 million km², the rainfall deficit varied between 10% and 30% from 1968 to 2010 despite the slight increase during the last two decades (Figure 4; Dia & Duponnois, 2013) with various regional modulating factors, such as ocean surface temperature or land use change (Giannini, Salack, Lodoun, Ali, Gaye, & Ndiaye, 2013).

Human-ecological interactions (soil types, farmland extensions, pastoral activities) are co-influencers of land dynamics and have an amplification effect on climate impacts (Mbow, Mertz, Diouf, Rasmussen, & Reenberg, 2008; Reenberg, Maman, & Oksenc, 2013; Mbow, Brandt, Ouedraogo, de Leeuw, & Marshall, 2015). Because of combined effects of land use and climate variability, land degradation—defined as the diminution or loss of biological or economic productivity—has been severe in the Sahel (Mbow, Rasmussen, Nielsen, Sambou, & Wardell, 2006), and is amplified by heavy wood extraction, forest clearing for agriculture, and overgrazing (Mbow et al., 2008; Ouedraogo, Mbow, Balinga, & Neufeldt, 2015). The rainfall deficit of the Sahel resulted in scores of impacts on forest resources, agriculture, and animal and human health, and subsequent impacts on natural-resources-dependent livelihoods, leading to massive rural to urban migrations (Mertz, Mbow, Reenberg, & Diouf, 2009). The known and most spectacular implications of this climate variability are large-scale famines and various kinds of recurrent food deficit (Djurfeldt, Hiolmen, Jirstrom, & Larsson, 2005).

Recent studies have nevertheless identified some positive trends in land dynamics. A set of unexpected positive trends was traced on greenness and tree cover (Dardel, Kergoat et al., 2014a; Kaptué et al., 2015; Mbow et al., 2015), on water flows in rivers (Dardel, Kergoat et al., 2014b), and on rainfall (Mbow et al., 2015; Tagesson, Fensholt, Guiro, Rasmussen, Huber, Mbow et al., 2015). Some of these trends nourished the debate on the so-called Sahel paradox, such as the observed increased primary productivity during the last two decades, mostly related to average rainfall improvement despite high climate variability (Brandt, Hiernaux, Tagesson, Verger, Rasmussen, Diouf et al., 2016; Dardel, Kergoat et al., 2014a; Kaptué et al., 2015). The constant picture in the Sahel, however, is one of a high climate variability and increased pressure on humans and on livestock, which does not favor a steady establishment of significant tree cover to prevent austere land degradation. Hence, prototyping desertification and land degradation has gained a great drive in using the Sahel as an example of productivity loss, soil erosion, water deficit, drought, high temperatures, and surface albedo change.

It is against this background of conspicuous and multifaceted land degradation that the Great Green Wall (GGW) initiative emerged¹ as a pan-African program to “green” the Sahel from west to east to combat the adverse effects of land degradation and desertification and to improve livelihoods. The underlying emphasis is on tackling the problems of poverty and of degradation of soil productivity throughout the entire Sahel-Saharan region, a strip of land 15 kilometers wide that stretches 7,100 kilometers from Dakar to Djibouti. The initiative is based on three-action agenda: the protection, conservation, and valorization of natural resources through the rehabilitation of degraded lands.

The GGW was officially established in an Official Decision of the African Union during a January 2007 Summit in Addis Ababa.² The coordination of the GGW is now established in Nouakchott (Mauritania) since 2014. The initiative has currently a clear governance structure, a well-established Pan-African secretary, and national agencies to address this complex, cross-sectoral, and ambitious undertaking, spanning the 11 participating Sahelian countries in 2017 (with many countries now joining) to reduce poverty and improve food security by reducing land degradation. The initiative has specific goals that include contributing to halting desertification and land degradation in the Sahelian zone, improving the lives and livelihoods of smallholder farmers and pastoralists in this area, and helping these vulnerable populations to adapt to and mitigate climate change through the tree-based development program. The approach of the GGW has evolved from the initial conception of a continuous “green wall” of dense trees—a defense line inspired by the Great Wall of China—to a more integrated-landscape approach to sustainability. The aim has since shifted toward ensuring, by 2025, an integrated approach to rural development that minimizes deforestation and land degradation while promoting local development around the Sustainable Development Centers.

Human and Geographical Context

Sahel is an Arabic word that refers to the fringe between the Sahara and the woodlands of the southern part. It is located roughly between 11⁰-N and 18⁰-N and experiences a strong north–south rainfall (200–800 mm/y) and vegetation (steppes to woodlands) gradients (Figures 1 and 3). The Sahel stripe cuts across major water basins (Senegal, Niger, Gambia, Volta, Lake Chad, and the Nile) and represents a high diversity of ecologies, ethnicity, and livelihoods. The region is dominated by pastoral activities and agriculture; other land uses include irrigation agriculture around water bodies, agroforestry, and conservation areas. In particular, pastoralism is clearly the major productive activity that values resources in arid and semi-arid parts of the Sahel, with secular practices preserved through long tradition of transhumance. The driest areas in the northern limit are generally dominated by the rangelands, where pastoralism directly engages 50 million people living on 1.8 million km2 of rangeland (35% of the whole Sahel; PRAPS, 2016). It is therefore important for the GGW to secure conditions for mobility for pastoralists while also managing the various pressures on resources to improve and maintain biodiversity, land health conservation, and farmers’ management of natural regeneration.

The wetter areas toward the south of the Sahel are dominated by agriculture combined with livestock breeding and cash-crop agriculture (ground nuts and cotton). The “dry frontier” of cultivation is often located in the vicinity of the 300 millimeters of annual rainfall isohyet separating roughly pure sylvipastoral systems with agrosylvipastoral systems (Turner & Hiernaux, 2002; Figure 1). Since colonial times, most of the Sahelian countries have had established laws designed to demarcate the frontier of agriculture vis-à-vis the pastoral zone (e.g., Senegal, Niger) as a land-management rule (Reenberg et al., 2013). Nevertheless, some parts this transition zone may be better described as a wide-ranging shift from pure rangeland to mosaic land use combining pastures and cropland. Hence, the crop- and livestock-production systems are to a large extent integrated: pastoralists often cultivate a little land, and farmers often have some livestock.

The mixed land use hints at the need to perceive the Sahel beyond its pastoral or agricultural systems and to embrace integrated environmental approaches that address multifunctionality and cover ecosystem services, biodiversity conservation, and the mitigation of climate change (Minang, van Noordwijk, Freeman, Mbow, de Leeuw, & Catacutan, 2015; Rasmussen & Reenberg, 2013). This conception of diverse landscapes and resource use is well suited to address the multiplicity of the driving forces of land dynamics (Geist & Lambin, 2002; Lambin & Ehrlich, 1997).

Additionally, recent dynamics in the Sahel require a full consideration of the role of the private sector, not only to scale up good practices for a greener Sahel, but also to anticipate any ecosystems that are being ill managed because of large-scale private investment in agriculture along the big rivers (Senegal, Niger around Lake Chad) to produce sugar cane, rice, fruit trees, and so on. The GGW cannot reasonability achieve its regional goals for ecosystem and livelihood improvement without seriously considering a clear engagement with the private sector.

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Figure 1. Livelihoods along a north–south transect from the Sahara to the humid tropics of West Africa. Note that this diagram does not include high land livelihoods. Horizontal arrows show changes in land agriculture practices; vertical arrows indicate geographical transitions of certain activities. The graph indicates the importance of the Sahel for other ecologies and the significant and complex livelihoods in place.

The GGW: From Awareness to a Pan-African Program

Combating desertification remains one of the most important and daunting challenges facing the sustainable development agenda. Desertification, land degradation, and drought are very much related in Africa’s drylands and constitute a complex phenomenon with which it is very hard to cope in a context of endemic poverty. The United Nations Convention to Combat Desertification (UNCCD), which was adopted in 1994, emphasized a change in the land-management concepts and practices in the drylands. Most importantly, the practical implication of the definition of desertification should lead to policy-relevant actions where desertification should not be perceived as steady desert encroachment. Rather, land dynamics leading to deserts appear wherever anthropogenic pressure—caused by unsustainable practices—outstretches fragile, and therefore vulnerable, natural resources (Thomas & Elias, 2014; Verstraete, Scholes, & Smith, 2009).

Coping adequately with desertification depends largely upon local conditions. The physical and socioeconomic conditions, including poverty, food insecurity, water shortage, health problems, and conflicts will determine what priority activity will be developed in various contexts (Dia & Duponnois, 2013). There is no denying that after the UNCCD was adopted in 1994, much has been done on various fronts in Africa, including the elaboration of national or regional programs to combat desertification and an improved understanding of the impacts of the land-productivity loss (Verstraete, Brink, Scholes, Beniston, & Smith, 2008). Despite the ambitions and the significance of many of these achievements, considerable challenges remain and require a serious and adequate response to the severe land degradation in the Sahel. For instance, not much has been done to incorporate pressing environmental issues, such as the fight against desertification, in development and poverty-reduction strategies. Similarly, the gender dimensions and equity issues, such as secure land tenure to all, remain considerable barriers in the Sahel. Poverty and the precariousness of most African economies also constitute a considerable barrier. In order to face the challenges and overcome the constraints on the effective and efficient implementation of the convention, a new impetus is needed, notably in the field of institutional innovation and governance (Dia & Duponnois, 2010). Having a pan-Africa effort as a framework through the GGW is certainly a unique example of that kind to address transboundary challenges.

Given the persistent severe climate conditions, the challenge becomes not only more urgent but bigger in scope, with the very uncertain rainfall making it difficult to sustain ambitious policies to combat land degradation. Decades of declining rainfall, combined with extreme events such as drought, flooding, extreme temperatures, and uneven rainfall distribution have impacted the population in the Sahel, who have suffered the negative effects of climate variability like no one else in the world. Combined with rapid demographic growth (projected to double by 2025), an even more severe humanitarian crisis due to food scarcity is expected in the Sahel.

The countries affected have initiated many programs in the past with specific goals for meeting these challenges. The vision of GGW is to use the regional-cooperation framework established by previous intergovernmental bodies and use the coverage of African Union (AU) to develop the program. Prior to the GGW, many attempts to coordinate regional interventions were established in West Africa and motivated by Economic Community of the West African States (ECOWAS) through, for instance, the CILSS (Permanent Interstates Committee to Control Drought Control in the Sahel) community, or the OSS (Sahara and Sahel Observatory; see Box 1). The GGW vision is based on a portfolio of activities that aims at improving rural livelihoods through land management and tree cover; establishing and managing water points; supporting farming practices and livestock breeding; developing rural infrastructure and promoting cash-generating activities to combat desertification and climate change. Box 1 shows few examples of these regional endeavors.

The Layout of the GGW, Ecologies, and Land Dynamics in the Sahel

The original discussion about the layout of the Sahel was purely a human-environmental one: the ability to grow trees on the soils, minimum rainfall, tracking the history of primary productivity using satellite data, determining the suitability for local community, and the possibility of deploying conservation strategies, including water body’s management and proximity to human settlements. Figure 2 shows the layout based on these criteria. With the evolution of the program, the GGW becomes more a concept that many countries beyond the Sahel have embraced, and some countries with higher rainfall are now engaging in the process, including southern African countries who are part of the African Union. Hence, the indicative layout does not consider the patch of GGW-related activities that are beyond the Sahel stripe.

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Figure 2. Layout of the Great Green Wall, based on decadal Normalized Difference Vegetation Index (NDVI), composite and rainfall.

Because of the importance of natural resources in the rural Sahel, the appropriate understanding of ecosystems and land-cover change is paramount for the GGW and raises the issues of context-specific land restoration and of the efficiency of land management for sustainable development.

The Sahel spans two broad biomes, which are the Sahel stricto sensu zone and Sudanian zones (Figures 1, 3, and 4)

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Figure 3. Land-cover map in the Sahel zone. Source: From GLC 2000, EU-JRC data.

The Sahelian zone is characterized by large, flat plains, riparian forests along rivers (e.g., the Senegal, the Niger), sand dunes, and outcrops of rocks or laterite. The large stretches of plain are mainly used for grazing and extraction of tree-based products (food, medicine, fodder, and wood) and smaller areas used for the cultivation of sorghum, beans, and millet, mostly in depressions and around water bodies. Much of the Sahel is dominated by rangelands with annual grasses of the Poacea and Fabaceae families that are very prone to seasonal fires (Sow, Hély, Mbow, & Sambou, 2013).

The Sudanean zone is characterized by a mosaic of woodlands and savanna intertwined with hotspots of biodiversity in gallery forests along rivers. Most of the zone is under cultivation, but there is very significant pastoral activity as well. There are important reserves of natural vegetation that are highly fragmented by moving fronts of agriculture and migrant farmers (e.g., southeastern Senegal, Southern Burkina Faso; Herrmann & Tappan, 2013; Mbow et al., 2008; Ouedraogo, Mbow et al., 2015). The area is undergoing serious decline in tree density and biodiversity related to rapid land-degradation processes (Gonzalez, Tucker, & Sy, 2012). An increase of grasses and shrubs at the expense of large trees is very common in many areas.

Increased population density raised the demand for natural products and intensified the pressure on land resources. A breakdown of land-dynamics factors shows a diversity of slow- and long-term drivers mostly related to farmers’ responses, choosing to expand or abandon unproductive lands, or even to relocate. In some cases, new areas of farm land are authorized by the government (e.g., the Pioneer Front in Senegal), local authorities, or by other institutions, as well as by outside investors, who acquire user rights to the land (Cotula et al., 2009). The population is still growing by more than 2% per year in the whole Sahelian countries; rural-to-urban migration is increasing, and the economics of crop production and animal husbandry has been impacted by fluctuating prices on inputs and products (external drivers). Given the human appropriation of biomass for food, feed, and other livelihood needs, the footprint of human interventions in the Sahel has been obvious at local scales (Krausmann, Erb, Gingrich, Haberl, Bondeau, Gaube et al., 2013).

Furthermore, the institutional setting has profoundly changed in most countries as a result of devolution processes, with new land-tenure systems in both croplands and rangelands influencing perceptions and practices of natural resource management (Figure 5). These human aspects are modulated by change in rainfall and soils fertility dynamics, legal and administrative frameworks or markets factors (Rasmussen & Reenberg, 2012).

Table 1. Pictured illustration of dominant landscapes in the Sahel

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Vegetation type	Examples of species	Rainfall range
	Boscia senegalensis; Acacia raddiana/tortilis; Calotropis procera; Leptadenia pyrotechnica; Salvadora persica	200-300 mm/y
	Acacia raddiana/tortilis; Acacia Senegal; Acacia nilotica; Boscia angustifolia; Balanites aegyptiaca; Calotropis procera; Leptadenia pyrotechnica; Grewia tenax; Acacia laeta; Acacia mellifera; Salvadora persica; Petrocarpus lucens	300-400 mm/y
	Combretum glutinosum; Commiphora Africana; Ziziphus mauritiana; Acacia macrostachya; Acacia nilotica; sclerocarya birrea; Adansonia digitata; Cordyla pinnata; Detarium senegalense	400-600 mm/y
	Combretum glutinosum; Terminalia macroptera; Piliostigma reticulatum; Grewia bicolor; Tamarix senegalensis; Vitellaria paradoxa; Ficus sp; Crossopterix febrifuga; Lannea acida; Bombax costatum; Strichnos spinosa; Pterocarpus eurenaceus	600-800 mm/y

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The Sahel was documented as showing a positive trend in the Normalized Difference Vegetation Index (NDVI; Fensholt, Langanke, Rasmussen, Reenberg, Prince, Tucker et al., 2012; Kaptué et al., 2015, Tagesson et al., 2015) with recent trends showing a mixed picture with some spots of severe degradation (Bégué, Vintrou, Ruelland, Claden, & Dessay, 2011; Mbow et al., 2015). Most studies agreed about this re-greening in the 1982–2002 period, and all were based on NOAA-AVHRR (National Oceanic and Atmospheric Administration—Advanced Very-high-Resolution Radiometer) products. Recent trends based on MODIS (Moderate Resolution Imaging Spectroradiometer) data (2000–2013) showed less agreement with various “browning” spots (Tagesson et al., 2015).

Given the close relationship between vegetation productivity and rainfall in the Sahel, important impacts of higher climate variability in the vegetation cover can be anticipated (Dardel, Kergoat et al., 2014a, 2014b; Meroni, Rembold, Verstraete, Gommes, Schucknecht, & Beye, 2014). Negative productivity left the population deprived and with limited resources for survival during the past megadrought events (1970s, 1980s).

Climate Challenge and Land Degradation: Need for Action

Given the close relationship between vegetation productivity and rainfall in the Sahel, large anomalies of biomass productivity have been documented (Brandt, Mbow, Diouf, Verger, Samimi, & Fensholt, 2015; Tian, Brandt, Liu, Verger, Tagesson, & Diouf, 2016). Rainfall levels were very high between 1950 and 1965, followed by a long series of droughts beginning in the 1970s, with a very slight improvement during the last couple of decades (Figure 4). Changes in rainfall can directly affect land productivity and indirectly dictate farmers’ choices for land use.

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Figure 4. Sahel precipitation anomalies 1900−2013. Although rainfall has somewhat recovered from its major drought in the mid-1980s, the level of rainfall is still below the values during the wet 1950s. Source: Joint Institute for the Study of the Atmosphere and Ocean, University of Washington.

Impacts of rainfall variability are more serious in low-rainfall areas (Sahel) than in higher rainfall of the Sudan zone. The climate regime that controls rainfall in West Africa is complex and instable. Because of this complexity, there is little agreement among the broad range of climate models used to predict future climate change in the area. Levels and patterns of seasonal rainfall profiles (seasonal length, frequency of dry spells) are strongly variable, but temperatures are continuously rising, aggravating other climate impacts (Borona, Mbow, & Ouedraogo, 2016). Using the Coupled Model Intercomparison Project-CMIP5, (Bathiany, Claussen, & Brovkin, 2014) concluded that some Sahelian greening is likely to occur, but the models do not agree on the timing and the processes that might cause the greening. There are various levels of uncertainties on the future trends as derived from climate and nonclimate forces.

On the land-health side, the Sahel is generally known for its hypersensitivity to wind and water erosion, but also to human land use practices (grazing and agriculture). The loss of the soil top layer creates a wide exposure of outcrops where infiltration becomes very minimum. One of the paradoxes of the Sahel is the increase of water runoff despite the very instable and decreasing rainfall patterns. This is the result of soil-quality change over time, with serious outcropping of hard surface exposures. Water does not infiltrate and flows rather rapidly, leading to the loss of soil moisture and therefore productivity. The runoff increases, which means a lot of suspended particles in the water ponds, and changes the water quality in the basins. This is known as the “browning” (referring to the color of the water) of the surface water in the Sahel with many heath implications.

Improving soil permeability is a an important ambition than can only be fulfilled through large-scale tree recovery. This is known as the biological approach (Perez, Albergel, Diatta, Grouzis, & Sene, 1997, 1998). The ecological role of trees as buffers against erosion and climate impact has been widely documented in studies by the World Agroforestry Centre (ICRAF; Bayala, Kalinganire, Tchoundjeu, Sinclair, & Garrity, 2011). In many parts of the Sahel, slight recovery of green vegetation due to combination of human and climate factors has been described as the “Greening of the Sahel” (Garrity, Akinnifesi, F. K. Ajayi, Weldesemayat, Mowo, Kalinganire et al., 2010).

Land reclamation through mechanical approaches has yielded effective results in Burkina Faso, Mali, and Senegal. Example of actions on soil-water-holding capacity include Zai, stones lines and stripes, and half-moons. The challenge with these is that they require high maintenance and heavy labor. The effects of such methods are usually local, as compared to large scale tree recovery using biological methods that have many subsequent benefits for humans and the environment. Depending to the context, a set of practices can be combined to address various land-restoration needs (Table 2).

Table 2. Example of scalable practices for land restoration.

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Examples of practices that can be scaled up	Description
Managing water bodies for livestock and crop production (Cassou, Burkina Faso)	Improve water supply during dry periods; create additional dry season production such as micro irrigation; water harvesting for livestock and sustainable management of water resources; wood plantation around water bodies, etc. This activity has been very apparent in the GGW strategy but needs some investment for the long term.
Management of bush fires (Cassou, Burkina Faso)	The overuse of fire affects biodiversity and ecosystem services. Populations use fires to create a mosaic of habitat patches that allow some practices such hunting, gathering of savanna products, and grazing. Grazing can rapidly turn into overgrazing with excessive use of fire. Fires can create irreversible changes locally which, accumulated over large areas, can change land cover at a regional scale. With increased temperature and uncertain rainfall, fires are likely to increase in frequency and impacts.
Wood extraction	Wood extraction for local and international markets has affected the tree cover quite severely in many areas. With increased population mostly in urban centers and the large dependence to traditional energy systems based on wood or charcoal, this activity requires more attention in the GGW to reduce over extraction of wood.
Promoting tree plantation in farmland (Khombole, Senegal)	Various agroforestry practices (mostly nitrogen-fixing trees) can be a great success in the GGW because of their fit in traditional farming systems and the potential in the region. Agroforestry systems range from sylvipastoral systems to home gardens, alley intercropping, and biomass plantations. It can help mitigate poverty because of its benefits. Agroforestry can support land degradation measures for its biomass that provides soil organic matter while producing firewood and environmental services.
Zai technique (Burkina Faso)	This technique falls into the water harvesting category but Zai does more than that: it also allows for increased soil fertility when mulched with crop residues or harvested biomass. Its capacity to hold water and increase soil moisture will not only buffer long dry spells during the short rainy season but it also allows for recharge of the water table hence helping the overall tree cover around to increase. Yields in Zai farms are always better that in non Zai farms.
Reducing runoff (Ouahigouyah, Burkina Faso)	Most Sahel water is quickly lost because of heavy runoff. The lack of trees will limit the ability of hard surface to retain water that quickly flows into rivers. To reduce that effect, parallel lines of plough are made on the soil outcrops to allow for water to stay longer. The same effect is pursued with lines of stones disposed along isolines of altitude to increase infiltration.
Managing rangelands (Ferlo, Senegal)	Managing rangeland implies many actions such as zoning grazing zones, creating corridors for transhumance, insuring water bodies for livestock, and reducing impacts on fodder. A full consideration of pastoral systems in the GGW will be a key success criteria not only for insuring greening activities but also for poverty alleviation and resilient socio-environmental systems.
Promoting fodder trees (Dahra, Senegal)	In the Sahel the rainfall is only 3 months at best in the northern part. In that particular area, small ruminants not often involved in long distance transhumance rely on fodder trees for fresh feed. Many acacia trees have a very good nutrient value for animals. The benefits of these fodder trees are their evergreen life form and their ability to tap into the ground water to survive droughts.

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Pursuing land-health ecologies in the GGW program requires advanced and wide-scale water harvesting and management. The implementation of the program in low-rainfall zones cannot be successful without a clear articulation of sustainable water management. The integrated approach adopted by the GGW requires a clear connection between land management and water management. It is clearly stipulated in the program’s overall goals the need to establish water harvesting to improve crop and livestock production while supporting regreening activities. Small water bodies are of particular importance for dry-season water supply for livestock and, in some cases, wet- and dry-season agriculture, with increased horticultural activities around these humid spots. Because of clogging by sediment accumulation, high temperatures leading to severe evapotranspiration, and infiltration, the capacity of these ponds to sustain livelihoods is very limited each year. The initiative strives to improve the water capacity of these ponds and microdams and to support their management with community by-laws and planning.

On a larger scale, integrated watershed management is central to the sustainable landscape approach and could build on lessons learned from transboundary water-resource management, such as the ones developed in the Senegal River Basin Development Authority (OMVS) or the Volta Basin Authority. The aim of watershed management is to protect water quality and optimize its use to support efforts of erosion control, improve infiltration, and favor the reforestation of degraded lands. The success in water resources management will also be tighten to mechanical and biological soil protection. Land that is sensitive to erosion will be preserved through integral protection and the plantation of resistance pioneer plants to reduce runoff.

More specifically, the population in the Sahel is striving to recover land productivity through such techniques such as the well-known Zai, although as of 2017, this method is mainly being used in Burkina Faso, Mali (where it is called Tassa), and Niger (Towalen). It consists of pitting the soil with wide holes to capture water and nutrients to allow plants to grow, even during severe dry spells during the humid season. The holes break the outcrop, improve water infiltration, and reduce runoff and erosion. The practice is usually combined with mulching in order to quickly recover the hydro-physical properties of degraded lands through vegetation biodiversity recovery. The sustainable recovery of soil properties without using mineral fertilizers is a particularly suitable in poverty conditions. Moreover, the use of Zai and mulch is limited by availability of organic matter (farm residues) used mostly to feed the livestock. Both techniques are highly demanding and time-consuming and are therefore the least-favored options in many communities that are so poor they opt for easier and cheaper solutions. A similar effect is pursued through the so-called half-moon, which is a kind of microdam through soil digging to create small floods where plants can grow.

Another important and locally adapted approach is agroforestry, the use of trees in farmland and pastoral land to improve soil fertility. Agroforestry is well-known to maintain or increase soil organic matter and biological nitrogen assimilation from nitrogen-fixing tree species (e.g., Faidherbia albida, Guiera senegalensis, Piliostigma reticulatum) are planted. Farmers maintain trees on their farms through Farmer Managed Natural Regeneration (FMNR) to trigger nutrient cycling and improve food production (Garrity et al., 2010). Trees’ ecological functions of tapping water and nutrients (acting as biological pumps) leached from the surface into the subsurface give them the ability to play the role of surface mulch that replenishes nutrients, conserves soil moisture, and improves soil organic matter (Bayala et al., 2011). In integrated land management, perennial plants play a key role in successful annual cropping by improving soil fertility. Agroforestry becomes therefore a key element in supplying household subsistence needs through the products and environmental services (e.g. fuel wood, fodder for livestock, food such a fruits and gums) and an adequate response to many adaptation and mitigation to climate change needs (carbon sequestration, shadow for crops, soil improvement, soil humidity in farm land, carbon restoration in soils, etc.) (Mbow, Smith, Skole, Duguma, & Bustamante, 2014).

Wood extraction is a major impediment to maintaining or establishing the tree cover in the Sahel, where communities are highly dependent on wood for energy. With growing urban populations and increased demand for wood products, the competition on wood resources is higher than the natural recovery of trees. Wood biomass loss also is linked with farming practices involving the selective clearing of stumps to allow for adequate crop growth (by increasing sunlight and making it easier to use rudimentary farm equipment). The harvested biomass is often burned to allow for rapid mineralization, but it is proven that slow and natural decaying can improve soil’s quality in the long term. After the early phase of land clearance, when only stumps may be preserved, valuable species are allowed to regenerate. Fuelwood is harvested only from branch wood or dead wood to preserve woody cover. This practice can be optimized to allow for a balance between soil organic matter and farming requirements.

Other natural-resources-management options include development of community mobilization as an alternative to unsuccessful centralized land-management policies of the past (Butzer, 2012). For a very long time, central-government-based policies eroded through failure to deliver community expectations. The laws established and constrained approach has demotivated local communities, which in most instances found the pace for engagement nil, yet posing a serious equity and stewardship issue in accessing and managing sustainably the resources they contributed to preserve for centuries. In the early 21st century, the approach is now toward community-based resources management; this nevertheless exposes the GGV initiative to the need for complex trade-offs to balance competing uses of land for rain-fed crops, irrigation agriculture, wood-energy extraction, agroforestry products, and especially pastoral activities.

Using land resources to address communities’ needs faces the emerging trend of land leasing in the Sahel. Some attempts to proceed with land privatization have led to the serious problem of land grab in many ecology-rich areas that are around the well-watered areas along rivers and floods for food production to export, bioenergy crops, fruit trees for agribusiness, and so on (Mbow, 2010). Since most agricultural and pastoral lands in the Sahel are still owned by the state, the state can, however, still allocate large areas to private investors, when they find it opportune. Few examples of this exist, yet it may become more relevant as external demands for land for biofuel production and carbon sequestration increase. The national legislation on ownership and users’ right to land is still being debated and not yet final, so the future legal basis for state-controlled allocation of land is unknown in the GGW path.

The processes of land allocation to private companies have been unclear and in most cases rejected by communities who reclaimed their ancestral lands (in Senegal serious social unrest was noted in 2011 in Fanaye Dieri, in the north, and in the Mopti area of Mali). Land privatization of will fail in most places in the Sahel because of the plurality of usages and the multifunctionality of the landscapes for various stakeholders. The GGW could be a framework for addressing the dual need for investment capital and poverty reduction through public-private-population partnerships.

Another challenge of the GGW will be to harness regional peace through the program. Resource scarcity in the Sahel resulted in many open conflicts between various groups. One of the highlights of the last thirty years has been the increase and diversification of land conflicts in the Sahel, largely related to the increase of the drought, but also in connection with new land deals. The insecurity is amplified with recent extremism in the region putting at risk any investment on land management. Therefore, developing comprehensive integrated resources management, with clear and strong engagement by all stakeholders, could reduce conflicts over access to and use of natural resources (Bonnet, 2017). Participatory approaches are used by the GGW to develop activities in various sites. Each country has a strategic and operational plan that builds on a previous a long-lasting legacy of various land-management approaches (see Box 2).

The GGW project is exploring using local institutions to implement its operational goals. All the countries have their own strategies, and they all recognize the importance of giving more authority to local communities. The emerging framework for land-tenure management is through local government engagement. A long historical process has led to that situation (Figure 5).

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Figure 5. Trajectory of land-tenure management, inspired by the Senegalese case, which is similar to that of many West African countries.

Improving Tree Cover in the Sahel through Afforestation

Afforestation has been a major program in all countries in the Sahel since the drought of 1970s. The goal of these programs is to recover deforested areas and to prevent further deforestation in many areas. The results have been mixed. The concept of establishing a dense stripe of trees, in effect creating a “green wall,” was pioneered by urban mangers in the northern African countries to stop the evolution of sand dunes. In the Sahelian countries, there were major tree-planting programs for combatting land degradation. They all were centralized programs, and they all learnt good skills in developing nurseries and selecting trees for various ecologies.

After many years, however, these centralized programs did not reach their goals; the exclusive centralized approach, requiring a great deal of investment and heavy equipment controlled by forest departments, left local communities out of the process. The main objectives of these postindependence tree plantation programs were to produce timber and stabilize erosion-prone areas, such sand dunes, coastal dunes, or around water bodies. However, the persistence of forest cover losses required the inevitable involvement of communities to ensure sustainability.

A central aim of the GGW is to increase tree cover across the Sahel, in plantations and in shelter belts, but also on farms. This will need to be a fully participatory exercise, with planners, government agencies, farmers, pastoralists, and other interested parties coming together to achieve the goals. Landowners are the custodians of great amount of local knowledge and experience and are involved in many activities, from planning to inception and the implementation of recovery of degraded lands. Centrally made decisions concerning where trees should be and how they should be used often make little sense to land users, and as a result, often fail. Experience in the Sahel has shown that where policies and incentives are favorable, farmers have themselves encouraged the natural regeneration of trees, and vast areas are now under tree cover as a result (e.g., the parklands of Faiderbia albida in Senegal and Niger). The GGW seeks to replicate the policies and incentives that lead to success stories and encourage an extension of the areas under naturally regenerated trees.

Because previous afforestation programs were supported by donor aid, the community-based forestry program was in most instances aimed at implementing village woodlots. This dynamic helped lead to the broader concept of including a rural forestry component in an integrated land-management framework, where the participatory approach called for a massive community participation and increased accountability and stewardship by engaging local stakeholders in land-restoration actions. That dynamic was parallel with a decentralization process and increased local democracy. Nevertheless, because there were many shortfalls in terms of the financial resources needed to sustain the program and its technical underpinnings—pruning, domestication, genetic conservation, nurseries, fire management, and so on—the local communities did not always have skills needed in planning and monitoring the greening activities.

This participatory approach was an integral part of the Forest Action Plans initiated during the early 1990s from Senegal to Chad. Implementation of this policy was based on the following key elements: involving populations, making them accountable in the conservation management of natural resources; integrating forestry in rural development; regionalization; and decentralizing forest planning. A new dynamic involving locally oriented tree-plantation projects is inspired by lessons learned during that era and aims to address the issue of wood demand sustainably. As opposed from the first-generation polices in which energy replacement with subsidized gas was prevalent, new polices want to act on the supply and preference and not only on the demand of energy. World Bank–funded programs in Senegal, Mali, and Burkina Faso initiated forest resource assessment in the countries and encouraged subsequent forest management for adequate supply of wood energy without destroying the natural capital.

Integrated Landscape Management

The GGW spans a vast area and includes a wide range of ecoregions and landscapes. To be effective, it is essential that decision-makers and implementers persue and apply sound integrated-management approaches based on scientific information on the state of the land resources and on what sustainable land-management intervention means in various conditions and contexts. To that end, it is noted a semantic evolution of the GGW concept from a pure tree-plantation approach to a more integrated landscape-management program that has many implications on the programmatic activities. Integrated landscape management to improve tree cover provides a competitive advantage for livelihoods when, in particular, valuable trees are promoted to deliver the basic human needs for food, water, health, and shelter and cash return. Given that trees can help save energy, increase economic stability, and reduce pollution and erosion, they become a key element of resilience. The most disseminated concept in the GGW countries is the integrated natural-resource management (INRM) that flourished to help resource users, managers, and others to manage resources sustainably by considering, reconciling, and synergizing their various interests and activities.

Therefore, the GGW seeks to provide tools, concepts, and frameworks for allocating and managing land to achieve social, economic, and environmental objectives in areas where agriculture, pastoralism, and other land uses compete with environmental and biodiversity goals. The national GGW programs have been advanced in response to increasing societal distress about environment and development tradeoffs. In the early 21st century, the recent developments of GGW therefore strives to develop a framework for negotiating resources access and production, minimizing conflicts and co-learning for reducing growing pressures on land, water and other resources toward sustainability.

Conclusion

To reverse land degradation and address climate change challenges, previous land-management efforts based on sectoral approaches such as the reforestation did not result in the expected outcomes on the economic, social and environmental conditions of vulnerable Sahelian populations. The GGW took up the challenge by acknowledging that no individual country has sufficient technical, human, and financial resources deal with the major land degradation and climate change challenges on its own. Accordingly, there is an urgent need for a united, integrated, and coordinated approach.

The GGW solutions are stated as actionable options that can be tailored to improving system productivity or diversity, efficiency, resilience, value and profitability of farming, including the enabling mechanisms needed within diverse local contexts. To that end, there is a need for all stakeholders to support developing and implementing site-specific solutions that allow for iterative and continuous improvement in each member country and implementation sites. In this context, different GGW countries are activating various stakeholders’ engagement to insure an effective implementation of the program. The objectives are multifold, but they all appeal for tangible initiatives and actions designed to restore, rehabilitate, protect, and rationally manage natural resources as part of the fight against desertification and land degradation.

The development agenda of the GGW must include the scaling up of good practices and strive to create a portfolio of activities that address the multifunctionality of landscapes. From this perspective, there is a need to adapt development policies to shift from centralized approaches to more inclusive mechanisms and frameworks for action that support the GGW requirements. In this regard, there is an increased recognition that GGW could pave the way for the onset of a true sustainable development concept, as stipulated by the United Nations Sustainable Development Goals (SDGs). This means that major financial and political support should be demanded for environmental preservation and the fight against desertification, both of which should stand out as basic vectors of poverty reduction in the Sahel.

New policy frameworks favors the GGW ambitions at regional levels with the African Forest Landscape Restoration Initiative (AFR100) that aims at restoring 100 million hectares of degraded land by 2030. AFR100 engages communities and states to address the Bonn Challenge, and the Land Degradation Neutrality targets. These strategic objectives are well aligned with the requirement for actions toward resilient landscapes, climate change objectives, and biodiversity conservation or SDGs and the Paris climate agreement.

The recognition of community ownership has, for instance, helped Sahelian countries to minimize the potential conflicts between development and environmental goals. Considerable changes have been therefore noted in national environmental policies toward gradually shifting national strategies from a focus on large-capital intensive, single-sector projects toward a new emphasis on bottom-up, participatory, and multisectoral approaches.